The Gemara (Berachot 55b) states: Rabbi Zeirah said "Whoever
sleeps seven days without having a dream, is called a bad person."
Do you have any suggestions what did Maharsha say on this?

Dear Moshe Mayor,

As you may have noticed, Maharsha doesn't expound on this
statement. He cross-references the two places in Tractate Berachot
where this statement appears.

Rashi explains the basic idea as follows: Dreams are sometimes
Divine messages. Seven days without such a vision indicates that
the person is unworthy of Heavenly communication.

The Vilna Gaon has a different explanation: Life is like a dream,
ephemeral and fleeting. If a person senses this, he will focus
on the eternal purpose of life - studying Torah and doing mitzvot.
Someone who goes seven days without sensing that this world is
like a temporary dream has lost sight of the real purpose of life.

Why seven? Because for six days a person is busy pursuing a livelihood.
He can therefore be forgiven for losing sight of life's temporary
nature. But if he goes seven days - including Shabbat -
without focusing on spiritual pursuits, he has abandoned life's
real purpose.